How to add shortcode to show/hide press releases?

I coded this up quickly, based on Scribu’s writeup on script loading, might work for you or provide a starting point.

The plugin file:

<?php
/* 
Plugin Name: MO_expander_shortcode
*/  

class MO_expander_shortcode {
    static $add_script;

    function init() {
        add_shortcode('moexpander', array(__CLASS__, 'handle_shortcode'));
        add_action('wp_footer', array(__CLASS__, 'add_script'));
    }

    function handle_shortcode($atts, $content = null) {
        self::$add_script = true;
        // this is the part that formats the markup with your content.
        // change it however you like, just be sure to update the js and css files to reflect changes.
        return '<div><a href="#" class="moexpander">expand</a></div><div class="moexpander">' . $content . '</div>';
    }

    function add_script() {
        if ( ! self::$add_script )
            return;

        wp_register_script('mo-expander-script', plugins_url('mo-expander-script.js', __FILE__), array('jquery'), '1.0', true);
        wp_print_scripts('mo-expander-script');

        wp_register_style('mo-expander-style', plugins_url('mo-expander-style.css', __FILE__));
        wp_print_styles('mo-expander-style');
    }
}
MO_expander_shortcode::init();

the mo-expander-script.js file:

jQuery(document).ready(function(){
    jQuery('div.moexpander').hide();
    jQuery('a.moexpander').click(function(){
        jQuery(this).parent().next('div.moexpander').slideToggle();
        return false;
    });                 
});

the mo-expander-style.css file:

.moexpander{
/* style as you wish! */
}

Use:
Put them all in a folder in your plugins directory and then activate it via the plugins page.
Then in the editor, enclose whatever content you want hidden as follows:

[moexpander]Some text here which will be hidden in a div with a link to toggle it open/closed[/moexpander]

You can add as many instances on a post as you wish. I’ll have to look into adding the TinyMCE button later, I haven’t done that before.